ND 3500AG and ND 3500B what's different?

I saw in the shop here NEC ND 3500B, I bought 1 month ago NEC ND 3500AG
and I’m asking myself what is the different ! Anyone know it ?

Maybe the color of the faceplate?

In my opinion the “B” is a write error. I never heard something about a NEC 3500B.

“ND-3500B” is a model number made up by the shop or their distributor to differentiate between different physical variations of the drive. The B is probably for black. The drive will still be recognized as a ND-3500AG by Windows.